DESCRIPTION: This study will use a unique data base involving more than 50,000 fibrillation defibrillation episodes in dogs and calves, all of which has been acquired as percent success versus parameters of the electrical shock, but expressed from the time domain. The purpose of this study is to better evaluate, understand, and interpret the factors which determine the efficacy of electrical shock in achieving cardiac defibrillation, if the shocks are expressed in the frequency domain. This study will first convert time domain data to frequency domain data, and then assess the percent success of defibrillation shocks.